This invention relates to vehicle suspensions of the type having dampers with at least two selectable damping characteristics, one of which provides higher damping than the other. It further relates to such vehicle suspensions having controls effective to change the dampers to the higher damping mode when the vehicle is accelerating or decelerating so as to reduce vehicle body dive and lift due to the vehicle deceleration and acceleration.
The prior art shows a number of such suspension systems. For example, some systems are responsive to the application of vehicle brakes to change to the high damping mode and reduce anticipated body dive due to braking. Other prior art systems change to the high damping mode in response to such sensed vehicle parameters as vehicle speed, steering angle, transmission gear selection, and throttle position.
Another type of prior art system provides active force generation by pumping fluid in and out of fluid spring chambers associated with the suspension system to counteract vehicle body rolls about various axes. One particular such system, shown in U.S. Pat. No. 4,602,805 to Tanaka et al, issued Jul. 29, 1986, exhausts fluid from the front wheel fluid spring chambers and provides fluid to the rear wheel fluid spring chambers when vehicle acceleration is indicated by various combinations of vehicle speed, transmission gear mode and throttle velocity. This system is more complex and expensive and less energy efficient than a simple selectable damper system. In addition, to detect vehicle acceleration, this system compares each of vehicle velocity and throttle velocity with fixed references, which are independent of the other of these variables; and the system is thus too sensitive to throttle movement at high vehicle velocities, where a given throttle velocity produces a small vehicle acceleration and little body lift, compared with low vehicle velocities, where it will produce a significantly greater acceleration and body lift.